Most popular software products nowadays constantly go through revisions to fix “bugs” or add new features and functionality. To that end, each revision of a software product or component may require the addition of new files, the replacement of existing files with newer versions of files, and/or removal of a file. Once a vendor has isolated a software product problem and created a solution for the problem, they would want to put that fix into an update and make the update widely available to the customers. Software vendors have a business incentive to distribute software updates to customers as quickly and trouble-free as possible.
The Internet provides a channel for customers to obtain the latest updates for software products. The vendor sites on the Internet can be designed to make it very simple to discover and locate updated files for an application. The technical aspects of file downloading have mostly disappeared from the user's view, and are now typically handled by the operating system.
To minimize the size of the updates over the Internet, software companies utilize file patches, which contain only the changes that must be made to pre-existing files, rather than the whole files themselves. A patch assumes that the original file on the target system is of a specific state. “Patching” applies changes to that file to bring the file to a desired, usually newer, state. However, the file should be verified to be in the required condition. Otherwise, the patch may be incorrectly applied and the file may be damaged. If a file to be patched is in an unexpected state, the patch cannot be applied. In addition, if the client machine has a sub-component that has a newer version than the one about to be upgraded, a conventional installation may abort the whole installation, even though there might be other sub-components that have older versions.